[PYTHON] Cross-references in definitions leads to circular reference in api

Description

When generating a python client api from a swagger specification containing a cross reference, i.e. type A references type B and type B references type A - the resulting python client cannot be used.

Swagger-codegen version

2.3.1

Swagger declaration file content or url

{
    "swagger": "2.0",
    "paths": {},
    "definitions": {
        "MyType1": {
            "properties": {
                "friend": {
                    "$ref": "#/definitions/MyType2"
                }
            }
        },
        "MyType2": {
            "properties": {
                "friend": {
                    "$ref": "#/definitions/MyType1"
                }
            }
        }
    }
}

Command line used for generation

java -jar swagger-codegen-cli.jar generate -i python-swagger-bug.json -l python -o python-bug

Steps to reproduce

java -jar swagger-codegen-cli.jar generate -i python-swagger-bug.json -l python -o python-bug
cd python-bug
python
import swagger_client

gives an ImportError:

ImportError: cannot import name 'MyType1'

Related issues/PRs

Probably related to the javascript issue with circular references
https://github.com/swagger-api/swagger-codegen/issues/8037

Suggest a fix/enhancement

The MyType1 python file refers to MyType2 which in turn refers to MyType1 (which hasn't been initialized). Removing the import in MyType2 to MyType1 fixes the problem.
I suppose the code generator should keep track of the order of the imports in the dependencies and prevent the circular imports.

Reproduce the issue with python-swagger-bug.json using the stated swagger-codegen CLI command, then inspect the generated MyType1 and MyType2 Python modules and their imports. Confirm the fix by running import swagger_client successfully for the mutually referenced definitions.